Rare cancers are uncommon malignant tumors, often defined as cancers with an annual incidence of less than 6 cases per 100,000 persons. Although individually rare, in total, rare cancers are estimated to represent more than 20% of all new cancer cases. The management of patients with rare cancers is particularly challenging because late or incorrect diagnosis is common and their rarity impedes clinical research, leading to substantial uncertainty regarding optimal treatment strategies. The decision-making process for rare cancer treatment management is complex and challenging because it requires balancing the clinical benefit of a treatment regimen with life expectancy, patient values, treatment goals, comorbidities, and potential treatment-related adverse events in a setting of limited research evidence.